In the satellite broadcasting, there are instances where signals of two or more different polarizations (the linear and circular polarization with the linear polarizations being divided into vertical and horizontal polarizations and the circular polarizations being divided right-hand and left-hand circular polarizations) are sent from the same direction to a particular area. Therefore, it is desirable that in this area such signals of plurality of different polarizations can be received altogether.
In frequency converter circuits of receiving apparatus for receiving such satellite broadcast, those heretofore put in practice have been constructed as shown in FIG. 1. In other words, an OMT (Ortho-Mode Transducer) 3 is connected to an input waveguide portion 2 within a circuit proper 1. Connected to the OMT 3 are an A-system electric signal processing circuit 4 including a mixer circuit 11a and a B-system electric signal processing circuit 5 including a mixer circuit 11b. An A-system local oscillator 8a is connected to the mixer circuit 11a of the A-system electric processing circuit 4 and also a B-system local oscillator 8b is connected to the mixer circuit 11b of the V-system electric signal processing circuit 5. In this case, the oscillation frequencies of the A-system local oscillator 8a and the B-system local oscillator 8b are of the same frequency. Also, it is constructed so that the supply of power to the A-system electric signal processing circuit 4 and the A-system local oscillator 8a and the supply of power to the B-system electric signal processing circuit 5 and the B-system local oscillator 8b are provided externally of the converters respectively from an A-system output connector 6 and a B-system output connector 7 through their respective power supply circuits or an A-system power supply circuit 9a and a B-system power supply circuit 9b, respectively. As a result, in order to operate only one of the two systems, only one of the output connectors is supplied with power, whereas in order to operate the two systems simultaneously, the power is supplied through the output connectors of the two systems.
It is to be noted that in FIG. 1 numerals 10a and 10b designate high frequency (RF) amplifier circuits, and 12a and 12b intermediate frequency (IF) amplifier circuits.
Such conventional device is of the construction which incorporates the two converters in the circuit proper 1 and it must be said that it is irrational from the cost point of view to dispose within the same circuit proper as many as two local oscillators which operate at the oscillation frequency. Also, it is needless to say that although the two oscillators oscillate at the same frequency, it is difficult to make the oscillation frequencies exactly the same and the mutual interference and disturbance of the two kinds of oscillation outputs tend to present problems.